The driver of a speaker for an automotive audio system includes a plurality of magnetic coils wound around a common bobbin. Each of the magnetic coils is connected to one of a plurality of amplifiers each of which output an identical drive signal. By applying the common drive signal to each magnetic coil, the electromagnetic field created around the magnetic coil is enhanced approximately in proportion to the number of magnetic coils. Due to this increased electromagnetic force, a vehicle panel serving as a sound-amplifying medium can be satisfactorily and successfully driven so as to produce high-quality sound. The amplifiers are adapted to amplify the low-frequency components of the audio signal from a main amplifier.